Presently available pull-out spray faucets provide a conventional valve assembly for mixing water from hot and cold supply lines and sending it through a hose to a hand-held spray head. Such faucets are commonly used in beauty parlors and home bathrooms to enable one to wash hair at a lavatory. In addition, faucets of this type are found at the kitchen sink for cleaning food items and dishes.
Improper use of a pull-out spray faucet may contaminate the potable water supply lines. This condition occurs when the spray head is immersed in non-potable water, such as water filling a sink. If the faucet's mixing valve also is open and a negative pressure occurs in the plumbing system at the faucet, a back-flow or siphoning of water from the sink through the faucet and into the plumbing system may occur. This back-flow introduces unsanitary water into the potable water supply.
In light of this potentially hazardous and unsanitary condition, it is essential that a means be provided to prevent the water back-flow. Many pull-out spray faucets on the market today incorporate a check valve in their inlet lines. Such check valves allow water to flow in only one direction through the valve, from the supply lines out through the faucet hose and spray head. Any negative pressure in the supply lines, which would create a back-flow, causes the check valve to close preventing a siphoning of waste water should the spray head be immersed. Although under ideal conditions, such check valves provide a safeguard against back-flow, mineral deposits, rust and other particles within the water lines can cause the check valve to stick in the open position. In addition, the check valve sealing members eventually wear, age and corrode rendering the valve non-functional. Therefore, it is desirable to provide a secondary mechanism to prevent an unsanitary back flow condition.